let fs = require('fs');
let buf = '';

process.stdin.on('readable', function() {
    let chunk = process.stdin.read();
    if (chunk) buf += chunk.toString();
});

process.stdin.on('end', function() {
    let lines = buf.split('\n');
    let [x1, y1] = lines[0].split(" ").map(function(x){return parseFloat(x);});
    let [x2, y2] = lines[1].split(" ").map(function(x){return parseFloat(x);});
    console.log(Math.sqrt(((x1 - x2)**2) + ((y1 - y2))**2).toFixed(4));
});